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Reorganization of supramammillary-hippocampal pathways in the rat pilocarpine model of temporal lobe epilepsy: evidence for axon terminal sprouting.

Soussi R, Boulland JL, Bassot E, Bras H, Coulon P, Chaudhry FA, Storm-Mathisen J, Ferhat L, Esclapez M - Brain Struct Funct (2014)

Bottom Line: This hypothalamic nucleus, which provides major extracortical projections to the hippocampal formation, plays a key role in the regulation of several hippocampus-dependent activities, including theta rhythms, memory function and emotional behavior, such as stress and anxiety, functions that are known to be altered in MTLE.This reorganization, which starts during the latent period, is massive when animals become epileptic and continue to evolve during epilepsy.It is characterized by an aberrant distribution and an increased number of axon terminals from neurons of both lateral and medial regions of the SuM, invading the entire inner molecular layer of the DG.

View Article: PubMed Central - PubMed

Affiliation: INSERM, UMR 1106, Institut de Neurosciences des Systèmes - INS, 13385, Marseille, France.

ABSTRACT
In mesial temporal lobe epilepsy (MTLE), spontaneous seizures likely originate from a multi-structural epileptogenic zone, including several regions of the limbic system connected to the hippocampal formation. In this study, we investigate the structural connectivity between the supramammillary nucleus (SuM) and the dentate gyrus (DG) in the model of MTLE induced by pilocarpine in the rat. This hypothalamic nucleus, which provides major extracortical projections to the hippocampal formation, plays a key role in the regulation of several hippocampus-dependent activities, including theta rhythms, memory function and emotional behavior, such as stress and anxiety, functions that are known to be altered in MTLE. Our findings demonstrate a marked reorganization of DG afferents originating from the SuM in pilocarpine-treated rats. This reorganization, which starts during the latent period, is massive when animals become epileptic and continue to evolve during epilepsy. It is characterized by an aberrant distribution and an increased number of axon terminals from neurons of both lateral and medial regions of the SuM, invading the entire inner molecular layer of the DG. This reorganization, which reflects an axon terminal sprouting from SuM neurons, could contribute to trigger spontaneous seizures within an altered hippocampal intrinsic circuitry.

No MeSH data available.


Related in: MedlinePlus

Comparison of immunohistochemical labeling for VGLUT2 in coronal sections through the rostro-caudal extent of the dentate gyrus from control (a, b′) and pilocarpine-treated animals at 1 week (c, d′), 2 weeks (e, f′), 2 months (g, h′) and 12 months (i, j′). a′–j′ panels correspond to high magnification of the region outline in panels a–j, respectively. a–b′ In a control rat, VGLUT2 immunolabeling was present in the granular (G) and molecular (M) layers of the dentate gyrus (DG) at rostral (a) and caudal (b) levels. Virtually no labeling was observed in the hilus (H). At high magnification (a′, b′), VGLUT2 labeling included both punctate structures (representative examples pointed by arrows) and a diffuse labeling. The punctate structures, presumed axon terminals from the supramammillary nucleus neurons, displayed different patterns of distribution along the dorsal to ventral axis of the dentate gyrus (a, b). These terminals were concentrated in the supragranular layer (SGL) of the dorsal region of DG (a′) and were much sparser distributed throughout the inner molecular layer (IML) in the ventral DG (b′). The diffuse immunolabeling for VGLUT2 was observed in the inner and outer one-third of the molecular layer (a, b). c–c′ In a pilocarpine-treated rat at 1 week, a decrease of the diffuse immunolabeling for VGLUT2 was evident in the IML of the dorsal (c, c′) but not in the ventral (d, d′) DG. As in control (a′, b′), many VGLUT2-containing terminals (arrows) were present in the SGL of the dorsal (c′) and ventral DG (d′). e–f′ In a pilocarpine-treated rat at 2 weeks, the loss of VGLUT2 diffuse labeling was still evident in the IML of the dorsal DG (e, e′). In addition to the numerous VGLUT2-containing terminals (arrows) observed in the SGL, many of them were also present in the IML in the dorsal DG (arrows; e′) and ventral IML (arrows; f′). g–h′ In an epileptic pilocarpine-treated rat at 2 months, numerous VGLUT2-containing terminals (arrows) were present in the entire IML throughout the rostro-caudal (g, h′) extent of the DG. An apparent recovery of diffuse labeling was observed in IML of the dorsal DG (g′). i–j′ In an epileptic animal at 12 months, VGLUT2 immunolabeling was clearly different from that observed in control and pilocarpine-treated rats at 1 and 2 weeks but also from epileptic animals at 2 months. VGLUT2-containing terminals displayed a double-band distribution pattern, these terminals being located in the SGL and in the uppermost part of the IML (arrows). A marked loss of the diffuse immunolabeling for VGLUT2 was observed now throughout the entire rostro-caudal level in the IML including in the ventral dentate gyrus. H hilus, G granule cell layer, M molecular layer, IML inner molecular layer, Ctrl control, Pilo 1 week pilocarpine-treated animal at 1 week after SE, Pilo 2 weeks pilocarpine-treated animal at 2 weeks after SE, Pilo 2 months pilocarpine-treated animal at 2 months after SE, Pilo 12months pilocarpine-treated animal at 12 months after SE. Scale bars 200 µm in a, c, e, g, i; 500 µm in b, d, f, h, j and 10 µm in a′–j′
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Fig1: Comparison of immunohistochemical labeling for VGLUT2 in coronal sections through the rostro-caudal extent of the dentate gyrus from control (a, b′) and pilocarpine-treated animals at 1 week (c, d′), 2 weeks (e, f′), 2 months (g, h′) and 12 months (i, j′). a′–j′ panels correspond to high magnification of the region outline in panels a–j, respectively. a–b′ In a control rat, VGLUT2 immunolabeling was present in the granular (G) and molecular (M) layers of the dentate gyrus (DG) at rostral (a) and caudal (b) levels. Virtually no labeling was observed in the hilus (H). At high magnification (a′, b′), VGLUT2 labeling included both punctate structures (representative examples pointed by arrows) and a diffuse labeling. The punctate structures, presumed axon terminals from the supramammillary nucleus neurons, displayed different patterns of distribution along the dorsal to ventral axis of the dentate gyrus (a, b). These terminals were concentrated in the supragranular layer (SGL) of the dorsal region of DG (a′) and were much sparser distributed throughout the inner molecular layer (IML) in the ventral DG (b′). The diffuse immunolabeling for VGLUT2 was observed in the inner and outer one-third of the molecular layer (a, b). c–c′ In a pilocarpine-treated rat at 1 week, a decrease of the diffuse immunolabeling for VGLUT2 was evident in the IML of the dorsal (c, c′) but not in the ventral (d, d′) DG. As in control (a′, b′), many VGLUT2-containing terminals (arrows) were present in the SGL of the dorsal (c′) and ventral DG (d′). e–f′ In a pilocarpine-treated rat at 2 weeks, the loss of VGLUT2 diffuse labeling was still evident in the IML of the dorsal DG (e, e′). In addition to the numerous VGLUT2-containing terminals (arrows) observed in the SGL, many of them were also present in the IML in the dorsal DG (arrows; e′) and ventral IML (arrows; f′). g–h′ In an epileptic pilocarpine-treated rat at 2 months, numerous VGLUT2-containing terminals (arrows) were present in the entire IML throughout the rostro-caudal (g, h′) extent of the DG. An apparent recovery of diffuse labeling was observed in IML of the dorsal DG (g′). i–j′ In an epileptic animal at 12 months, VGLUT2 immunolabeling was clearly different from that observed in control and pilocarpine-treated rats at 1 and 2 weeks but also from epileptic animals at 2 months. VGLUT2-containing terminals displayed a double-band distribution pattern, these terminals being located in the SGL and in the uppermost part of the IML (arrows). A marked loss of the diffuse immunolabeling for VGLUT2 was observed now throughout the entire rostro-caudal level in the IML including in the ventral dentate gyrus. H hilus, G granule cell layer, M molecular layer, IML inner molecular layer, Ctrl control, Pilo 1 week pilocarpine-treated animal at 1 week after SE, Pilo 2 weeks pilocarpine-treated animal at 2 weeks after SE, Pilo 2 months pilocarpine-treated animal at 2 months after SE, Pilo 12months pilocarpine-treated animal at 12 months after SE. Scale bars 200 µm in a, c, e, g, i; 500 µm in b, d, f, h, j and 10 µm in a′–j′

Mentions: The pattern of VGLUT2 immunohistochemical labeling in the rat hippocampus has been reported previously (Fremeau et al. 2001; Herzog et al. 2001; Kaneko et al. 2002; Halasy et al. 2004; Boulland et al. 2009; Soussi et al. 2010). Our study focused on the dentate gyrus (DG) where the main differences were observed between control and pilocarpine-treated rats. A detailed description of VGLUT2 immunolabeling through the entire rostro-caudal extent of the DG was provided in control rats to compare to that of pilocarpine-treated rats. All control animals, regardless of their age, displayed the same patterns of immunolabeling for VGLUT2. In these control animals, the VGLUT2 immunolabeling showed both laminar- and regional-specific patterns within the DG (Fig. 1a–b′). At low magnification, whereas moderate to strong VGLUT2 immunolabeling were evident in the molecular and granule cell layers, very low levels or virtually no labeling were observed in the hilus and CA3c pyramidal cell layer, respectively, through the entire rostral (Fig. 1a) to caudal (Fig. 1b) extent of the DG. At higher magnification (Fig. 1a′, b′), the immunohistochemical labeling for VGLUT2 was characterized by large punctate structures (arrows) and by a thin diffuse labeling, as previously described (Fremeau et al. 2001; Kaneko et al. 2002; Halasy et al. 2004). The large punctate structures, observed through the entire rostro-caudal extent of the hippocampus displayed, however, different patterns of distribution along the dorsal to ventral axis of the DG. Whereas in the dorsal DG, these large punctate structures labeled for VGLUT2 were highly concentrated in the supragranular layer (SGL) delineating this narrow region superficial to the granule cells from the adjacent IML (Fig. 1a′, arrows), in the ventral DG, they were dispersed within SGL and adjacent IML (Fig. 1b′, arrows). These VGLUT2-labeled punctate structures correspond mainly to axon terminals from neurons located in the SuM (Boulland et al. 2009; Soussi et al. 2010). The diffuse VGLUT2 immunolabeling, observed in the DG, displayed a similar pattern of distribution along the rostro-caudal and dorso-ventral axes of the hippocampus with higher levels of labeling in the inner and outer one-third of the molecular layer (Fig. 1a, b). These diffuse labeling in the inner and outer one-third of the DG molecular layer has been suggested to correspond to axon terminals originating from hilar mossy cells and entorhinal cortex layer II/III neurons, respectively (Halasy et al. 2004).Fig. 1


Reorganization of supramammillary-hippocampal pathways in the rat pilocarpine model of temporal lobe epilepsy: evidence for axon terminal sprouting.

Soussi R, Boulland JL, Bassot E, Bras H, Coulon P, Chaudhry FA, Storm-Mathisen J, Ferhat L, Esclapez M - Brain Struct Funct (2014)

Comparison of immunohistochemical labeling for VGLUT2 in coronal sections through the rostro-caudal extent of the dentate gyrus from control (a, b′) and pilocarpine-treated animals at 1 week (c, d′), 2 weeks (e, f′), 2 months (g, h′) and 12 months (i, j′). a′–j′ panels correspond to high magnification of the region outline in panels a–j, respectively. a–b′ In a control rat, VGLUT2 immunolabeling was present in the granular (G) and molecular (M) layers of the dentate gyrus (DG) at rostral (a) and caudal (b) levels. Virtually no labeling was observed in the hilus (H). At high magnification (a′, b′), VGLUT2 labeling included both punctate structures (representative examples pointed by arrows) and a diffuse labeling. The punctate structures, presumed axon terminals from the supramammillary nucleus neurons, displayed different patterns of distribution along the dorsal to ventral axis of the dentate gyrus (a, b). These terminals were concentrated in the supragranular layer (SGL) of the dorsal region of DG (a′) and were much sparser distributed throughout the inner molecular layer (IML) in the ventral DG (b′). The diffuse immunolabeling for VGLUT2 was observed in the inner and outer one-third of the molecular layer (a, b). c–c′ In a pilocarpine-treated rat at 1 week, a decrease of the diffuse immunolabeling for VGLUT2 was evident in the IML of the dorsal (c, c′) but not in the ventral (d, d′) DG. As in control (a′, b′), many VGLUT2-containing terminals (arrows) were present in the SGL of the dorsal (c′) and ventral DG (d′). e–f′ In a pilocarpine-treated rat at 2 weeks, the loss of VGLUT2 diffuse labeling was still evident in the IML of the dorsal DG (e, e′). In addition to the numerous VGLUT2-containing terminals (arrows) observed in the SGL, many of them were also present in the IML in the dorsal DG (arrows; e′) and ventral IML (arrows; f′). g–h′ In an epileptic pilocarpine-treated rat at 2 months, numerous VGLUT2-containing terminals (arrows) were present in the entire IML throughout the rostro-caudal (g, h′) extent of the DG. An apparent recovery of diffuse labeling was observed in IML of the dorsal DG (g′). i–j′ In an epileptic animal at 12 months, VGLUT2 immunolabeling was clearly different from that observed in control and pilocarpine-treated rats at 1 and 2 weeks but also from epileptic animals at 2 months. VGLUT2-containing terminals displayed a double-band distribution pattern, these terminals being located in the SGL and in the uppermost part of the IML (arrows). A marked loss of the diffuse immunolabeling for VGLUT2 was observed now throughout the entire rostro-caudal level in the IML including in the ventral dentate gyrus. H hilus, G granule cell layer, M molecular layer, IML inner molecular layer, Ctrl control, Pilo 1 week pilocarpine-treated animal at 1 week after SE, Pilo 2 weeks pilocarpine-treated animal at 2 weeks after SE, Pilo 2 months pilocarpine-treated animal at 2 months after SE, Pilo 12months pilocarpine-treated animal at 12 months after SE. Scale bars 200 µm in a, c, e, g, i; 500 µm in b, d, f, h, j and 10 µm in a′–j′
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Related In: Results  -  Collection

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Fig1: Comparison of immunohistochemical labeling for VGLUT2 in coronal sections through the rostro-caudal extent of the dentate gyrus from control (a, b′) and pilocarpine-treated animals at 1 week (c, d′), 2 weeks (e, f′), 2 months (g, h′) and 12 months (i, j′). a′–j′ panels correspond to high magnification of the region outline in panels a–j, respectively. a–b′ In a control rat, VGLUT2 immunolabeling was present in the granular (G) and molecular (M) layers of the dentate gyrus (DG) at rostral (a) and caudal (b) levels. Virtually no labeling was observed in the hilus (H). At high magnification (a′, b′), VGLUT2 labeling included both punctate structures (representative examples pointed by arrows) and a diffuse labeling. The punctate structures, presumed axon terminals from the supramammillary nucleus neurons, displayed different patterns of distribution along the dorsal to ventral axis of the dentate gyrus (a, b). These terminals were concentrated in the supragranular layer (SGL) of the dorsal region of DG (a′) and were much sparser distributed throughout the inner molecular layer (IML) in the ventral DG (b′). The diffuse immunolabeling for VGLUT2 was observed in the inner and outer one-third of the molecular layer (a, b). c–c′ In a pilocarpine-treated rat at 1 week, a decrease of the diffuse immunolabeling for VGLUT2 was evident in the IML of the dorsal (c, c′) but not in the ventral (d, d′) DG. As in control (a′, b′), many VGLUT2-containing terminals (arrows) were present in the SGL of the dorsal (c′) and ventral DG (d′). e–f′ In a pilocarpine-treated rat at 2 weeks, the loss of VGLUT2 diffuse labeling was still evident in the IML of the dorsal DG (e, e′). In addition to the numerous VGLUT2-containing terminals (arrows) observed in the SGL, many of them were also present in the IML in the dorsal DG (arrows; e′) and ventral IML (arrows; f′). g–h′ In an epileptic pilocarpine-treated rat at 2 months, numerous VGLUT2-containing terminals (arrows) were present in the entire IML throughout the rostro-caudal (g, h′) extent of the DG. An apparent recovery of diffuse labeling was observed in IML of the dorsal DG (g′). i–j′ In an epileptic animal at 12 months, VGLUT2 immunolabeling was clearly different from that observed in control and pilocarpine-treated rats at 1 and 2 weeks but also from epileptic animals at 2 months. VGLUT2-containing terminals displayed a double-band distribution pattern, these terminals being located in the SGL and in the uppermost part of the IML (arrows). A marked loss of the diffuse immunolabeling for VGLUT2 was observed now throughout the entire rostro-caudal level in the IML including in the ventral dentate gyrus. H hilus, G granule cell layer, M molecular layer, IML inner molecular layer, Ctrl control, Pilo 1 week pilocarpine-treated animal at 1 week after SE, Pilo 2 weeks pilocarpine-treated animal at 2 weeks after SE, Pilo 2 months pilocarpine-treated animal at 2 months after SE, Pilo 12months pilocarpine-treated animal at 12 months after SE. Scale bars 200 µm in a, c, e, g, i; 500 µm in b, d, f, h, j and 10 µm in a′–j′
Mentions: The pattern of VGLUT2 immunohistochemical labeling in the rat hippocampus has been reported previously (Fremeau et al. 2001; Herzog et al. 2001; Kaneko et al. 2002; Halasy et al. 2004; Boulland et al. 2009; Soussi et al. 2010). Our study focused on the dentate gyrus (DG) where the main differences were observed between control and pilocarpine-treated rats. A detailed description of VGLUT2 immunolabeling through the entire rostro-caudal extent of the DG was provided in control rats to compare to that of pilocarpine-treated rats. All control animals, regardless of their age, displayed the same patterns of immunolabeling for VGLUT2. In these control animals, the VGLUT2 immunolabeling showed both laminar- and regional-specific patterns within the DG (Fig. 1a–b′). At low magnification, whereas moderate to strong VGLUT2 immunolabeling were evident in the molecular and granule cell layers, very low levels or virtually no labeling were observed in the hilus and CA3c pyramidal cell layer, respectively, through the entire rostral (Fig. 1a) to caudal (Fig. 1b) extent of the DG. At higher magnification (Fig. 1a′, b′), the immunohistochemical labeling for VGLUT2 was characterized by large punctate structures (arrows) and by a thin diffuse labeling, as previously described (Fremeau et al. 2001; Kaneko et al. 2002; Halasy et al. 2004). The large punctate structures, observed through the entire rostro-caudal extent of the hippocampus displayed, however, different patterns of distribution along the dorsal to ventral axis of the DG. Whereas in the dorsal DG, these large punctate structures labeled for VGLUT2 were highly concentrated in the supragranular layer (SGL) delineating this narrow region superficial to the granule cells from the adjacent IML (Fig. 1a′, arrows), in the ventral DG, they were dispersed within SGL and adjacent IML (Fig. 1b′, arrows). These VGLUT2-labeled punctate structures correspond mainly to axon terminals from neurons located in the SuM (Boulland et al. 2009; Soussi et al. 2010). The diffuse VGLUT2 immunolabeling, observed in the DG, displayed a similar pattern of distribution along the rostro-caudal and dorso-ventral axes of the hippocampus with higher levels of labeling in the inner and outer one-third of the molecular layer (Fig. 1a, b). These diffuse labeling in the inner and outer one-third of the DG molecular layer has been suggested to correspond to axon terminals originating from hilar mossy cells and entorhinal cortex layer II/III neurons, respectively (Halasy et al. 2004).Fig. 1

Bottom Line: This hypothalamic nucleus, which provides major extracortical projections to the hippocampal formation, plays a key role in the regulation of several hippocampus-dependent activities, including theta rhythms, memory function and emotional behavior, such as stress and anxiety, functions that are known to be altered in MTLE.This reorganization, which starts during the latent period, is massive when animals become epileptic and continue to evolve during epilepsy.It is characterized by an aberrant distribution and an increased number of axon terminals from neurons of both lateral and medial regions of the SuM, invading the entire inner molecular layer of the DG.

View Article: PubMed Central - PubMed

Affiliation: INSERM, UMR 1106, Institut de Neurosciences des Systèmes - INS, 13385, Marseille, France.

ABSTRACT
In mesial temporal lobe epilepsy (MTLE), spontaneous seizures likely originate from a multi-structural epileptogenic zone, including several regions of the limbic system connected to the hippocampal formation. In this study, we investigate the structural connectivity between the supramammillary nucleus (SuM) and the dentate gyrus (DG) in the model of MTLE induced by pilocarpine in the rat. This hypothalamic nucleus, which provides major extracortical projections to the hippocampal formation, plays a key role in the regulation of several hippocampus-dependent activities, including theta rhythms, memory function and emotional behavior, such as stress and anxiety, functions that are known to be altered in MTLE. Our findings demonstrate a marked reorganization of DG afferents originating from the SuM in pilocarpine-treated rats. This reorganization, which starts during the latent period, is massive when animals become epileptic and continue to evolve during epilepsy. It is characterized by an aberrant distribution and an increased number of axon terminals from neurons of both lateral and medial regions of the SuM, invading the entire inner molecular layer of the DG. This reorganization, which reflects an axon terminal sprouting from SuM neurons, could contribute to trigger spontaneous seizures within an altered hippocampal intrinsic circuitry.

No MeSH data available.


Related in: MedlinePlus